The present invention relates in general to network services based on the IP Multimedia Subsystem, and, more specifically, to the creation of partitioned (i.e., multiplexed) IMS services so that a customers of a network provider can obtain their own virtual IMS services without having to build their own infrastructure.
The Internet Protocol (IP) multimedia subsystem (IMS) is a standard developed by the 3rd Generation Partnership Project (3GPP) for the purpose of delivering IP-based multimedia communications across many types of access networks, including wireless (e.g., cellular or PCS) networks. IMS defines a session control layer that interfaces between an applications layer and a transport layer. The applications layer may include any packet-based media application including voice, video, data, and other content. The transport layer handles many different types of access networks including mobile wireless, ISP's, enterprise systems, and PSTN.
The session control layer uses pre-existing Internet protocols (e.g., the session initiation protocol, or SIP) for registering end-user devices and routing signaling messages between users and applications. Two main elements of the session control layer are the call session control function (CSCF) and the home subscriber server (HSS). The CSCF performs session set-up, modification, and termination through the interaction of a proxy CSCF (P-CSCF), an interrogating CSCF (I-CSCF), and a serving CSCF (S-CSCF). As the central node of the signaling plane, the S-CSCF is registrar for each user session with an application. It also handles authentication of the user. The P-CSCF is the user's entry point into the IMS domain. It protects the S-CSCF from direct exposure to the access networks, and all SIP messages pass through the P-CSCF during the entire session. The I-CSCF is a SIP function located at the edge of an administrative domain between the P-CSCF and S-CSCF. Its address is published in a DNS of the domain so that the user terminal can find it via the P-CSCF. The I-CSCF contacts the HSS to determine the correct S-CSCF associated with the user request, and then become the forwarding point for SIP messages during the session.
In a typical implementation, IMS is a network domain having various discrete elements performing the functions of at least the call session control functions and the home subscriber server. Whether implemented by a private enterprise or a public network provider, the IMS domain may also include 1) at least one application server in the applications layer, and 2) a media gateway control function (MGCF), a subscriber location function (SLF), and a policy decision function (PDF) in the session control layer. Due to the multitude of functional elements, it is expensive to create an IMS domain. Because of the high cost, an IMS core will only be created when its benefits justify the cost. For a telecommunications service provider, an IMS domain can enable the integration of wireless services with traditionally wireline-based services such as PBX. Calls to one single phone number assigned to a user will simultaneously ring their desk phone and cellular phone. Voicemail and other services are also integrated and accessible from either phone. By handling such applications in an all-IP network, the service provider obtains improved efficiency of service and it can more easily deploy many types of multimedia applications.
For an enterprise that is not a mobile service provider, the expense of an IMS domain often makes it impractical to create such a system. However, many such enterprises need to deliver multimedia applications to their internal and external users in a secure environment using IMS. Therefore, it would be desirable to extend the functionality of operating an IMS core to an enterprise without incurring the associated high costs.